Cellulose derivative and method of preparing same



Patented Dec. 5. 1939 UNITED STATES PATENT OFFICE OELLULOSE DERIVATIVEAND METHOD OF PREPARING SAME No Drawing. Application November 29, 1937,

Serial No. 177,157

28 Claim.

This invention relates to cellulose derivatives and to the preparationof such derivatives. A

more specific form of the invention relatesto cellulose xanthatesobtained by the action of a carbon bisulfide on anhydrous alkali metalcellulosates.

Alkali metal cellulosates, such as above referred to, are obtainableaccording to the invention described and claimed in my co-pendingapplications Serial No. 670,039 filed May8, 1933, and Serial No. 177,156filed November 29, 1937.

The preparation of cellulose xanthate has heretofore been accomplishedby steeping cellulose in a strong alkali solution, e. g., 18-20% causticsoda, pressing out the alkali solution to approximately three times theoriginal weight of the cellulose, disintegrating the alkali celluloseand allowing it to age for several days to obtain a reduction in theviscosity of the cellulose and finally treating the aged alkalicellulose with either liquid 'or vapor carbon disulfide. The wholeprocess is carried out in the presence of water or, rather, an aqueoussolution of caustic soda. The product so prepared is used in theformation of films, filaments, threads, etc., by dissolving in asolution of caustic soda and regenerating the cellulose by precipitationin an acid bath.

During the steeping of the cellulose in caustic solution and thesubsequent pressing out of the same, a loss in cellulose always occursdue to the fact that a portion of the cellulose dissolves in the strongcaustic and is lost when the excess caustic is removed. Furthermore, thecaustic soda which is pressed out cannot be reused indefinitely becauseit becomes contaminated with this dissolved organic matter and thereforehas to be discarded from time to time.

Cellulose xanthate prepared according to the prior art is an unstablechemical compound and in a few days changes to a form which isdiflicultly soluble in alkali solutions and must, therefore, be usedalmost immediately. The instability of ordinary cellulose xanthateprevents the possibility of shipping this material any considerabledistance before use except possibly in the form of a solution in alkaliwhich would be rather expensive. Another disadvantage to the commonlyknown type of cellulose xanthate is that solutions of this material aregenerally colored a deep orange due to the presence of certainby-products formed during the preparation of the cellulose xanthate.

This invention has for an object the preparation of a cellulose xanthateand other cellulosic derivatives, preferably under substantiallyanhydrous conditions, by a new method with avoidance of thedisadvantages heretofore encountered. A further object is theutilization of such cellulose xanthate or other derivatives in thepreparation of films, filaments, threads, etc.

These objects are accomplished by the invention to be now described.

Cellulose is converted to alkali metal cellulosate and preferably underanhydrous conditions as fully described in my co-pending applicationreferred to above. Briefly, my co-pending application describes aprocess wherein cellulose, which has been carefully dried, is contactedwith metallic alkali metal dissolved in liquid ammonia. Under suchconditions, one atom of hydrogen per Cs unit of cellulose is easily andrapidly replaced by one atom of alkali metal. One, two, or three atomsof hydrogen per Co unit of cellulose are found to be replaceable by suchprocess. The alkali metal cellulosate to be used in the present methodmay also be prepared by other methods, although the method described inthe above mentioned applications is preferred.

Having so formed analkali metal cellulosate, this cellulosate is causedto react with carbon bisulflde in the presence of liquid ammonia. Liquidammonia is then removed by decantation or by vaporization, or both, sothat a dry product results, this product being cellulose xanthate. Thedry cellulose xanthate may be dissolved in an alkaline solution and thecellulose regenerated by passing said solution through suitable acid orsalt baths.

The following examples will illustrate methods used to prepare cellulosexanthate.

Ezample 1 Three grams of dry cellulose from wood was suspended in about100 cc. of liquid ammonia and 0.65 g. of sodium (1.5 atoms per C6 unitof cellulose) was added. Thismixture was'stirred frequently until thedeep blue color, developed by the solution of sodium in liquid ammoniadisappeared; and then 1.1 cc. of carbon disulfide (1 mol per Cs unit ofcellulose) was added. The carbon disulfide in liquid ammonia formed ared color which was discharged when all the carbon disulfide had reactedwith sodium cellulosate. The excess liquid ammonia was then decantedaway or evaporated off and left the cellulose xanthate in the form oftheoriginal paper but colored a light yellow. The product was almostcompletely soluble in 6.5% solution of caustic soda and yielded a solidprecipitate when this 55 solution was added to a dilute solution of anacid.

Example 2 10 was very quickly discharged. One mol of carbon disulfidewas then added to the sodium cellulosate as in Example 1 and a reactionoccurred for the red color of the carbon disulfide was slowlydischarged. After washing out the sodium 15 iodide with liquid ammonia,the product which was left was very similar to the xanthate obtainedfrom the other example.

Example 3 Fifteen grams of purified cotton linters was covered with 500cc. of liquid ammonia to which was added 50 g. of dry sodium thiocyanateand 6.1 g. of sodium (2.65 atoms per Ce unit of cellulose). Under theseconditions the cellulose was very highly swollen and the blue colorentirely disappeared at the end of two hours. Thirty-three grams ofcarbon disulfide (3 mols) wasthen added and in 15 minutes the cellulosehad dissolved completely in the liquid ammonia,

3 to form a smooth viscose solution. In this case the xanthate wasrecovered by pouring the whole mixture into methyl alcohol which took upall the excess carbon disulfide and also removed the swelling agent. Theproduct was a white solid, which turned to a light yellow on standing,and was completely soluble in dilute caustic soda. On analysis thisproduct was found to contain 4.06% sodium and 9.55% of sulfur.

Example 4 Finely ground high alpha wood pulp was carefully dried andtreated in liquid ammonia with sufilcient metallic sodium to form adi-sodium cellulosate and allowed to stand until the blue color of thesodiumhad disappeared. The ammonia was then allowed to boil off under amercury seal and the product was placed in an oven at 70 C. for a shorttime to drive off the remainder of the ammonia. To 5 g. of the foregoingdry product was added 6.0 g. of water and 6.25 g. of CS2 and the mixtureallowed to react in a closed flask for 3 hours at ordinary roomtemperature. The product dissolved in dilute caustic to produce aperfectly smooth solution which was very similar to solutions ofcellulose xanthate made from soda-cellulose by the more usual procedure.

The preparation of threads from the above described cellulose xanthatesis accomplished by methods similar to those used in the prior art. Forexample, the cellulose xanthate is dissolved in a 5-7% solution ofcaustic soda and after filtering is coagulated and regenerated in anacid salt bath of the general type used in the viscose industry. Thisbath, for example, may contain sulfuric acid, 10% glucose, 12% sodiumsulfate, and 1% zinc sulfate.

The preparation of cellulose xanthate from sodium cellulose is notlimited to the conditions given in the examples, All types of cellulosesuch as cotton linters, sulfite wood pulp or any form of relatively purecellulose may be used. More- I for example, be aged as in the regularviscose process and the alkali washed out with water so that a swollenlow viscosity cellulose is obtained.

Swelling agents (NaI or NaCNS) may be used in varying amounts so thatthe cellulose may be only slightly swollen or brought almost completelyinto solution in the liquid ammonia.

These agents have the ability of speeding the formation of the sodiumcellulosate and the cellulose xanthate and their use in combination withan excess of sodium and carbon disulfide assists in the solution of thexanthate in liquid ammonia as illustrated in Example 3.

The atoms of sodium substituted in a C6 unit of cellulose may be anynumber up to 3 and the amounts of carbon disulfide used may vary from aabout one-half to three mols per Cs unit of cellulose. Better resultsseemto be obtained when using a highly substituted sodium cellulosateand at least 0.75 mol of carbon disulfide per Cs unit of cellulose. v

Metallic potassium may be used instead of sodium for the preparation ofthe alkali cellulosate.

The isolation of the final product may :'be accomplished in several wayssuch as by direct evaporation of the ammonia or by precipitation V in anon-solvent for cellulose xanthate of the type of methyl or ethylalcohol. Any excess carbondisulfide or swelling agent can be removed byrepeatedly washing with liquid ammonia or,

ifthe cellulose xanthate is precipitated in an organic solvent, theproduct'can be washed with the precipitating liquid.

In the examples given the formation of sodium cellulosate and cellulosexanthate was carried out in liquid ammonia at its boilingpoint and atatmospheric pressure or about 33 C. The process may be conducted athigher or lower temperatures, in which case it is only necessary tolulose and carbon bisulfidethe proportion of reactants can possibly bemade more nearly-theoretical than in the present commercial xanthationprocess. 1

It has been noted that cellulose xanthate prepared according to thisinvention is more stable than a regular xanthate as samples have beenkept three weeks without appreciable change and it is quite probablethat the stability of the new xanthate is even; greater than this. Afurther advantage ofthis product is the light color of the solutionprepared from it. This is due to the absence of colored by-products.

. A stable cellulose xanthate, prepared according to this invention, isutilizable as an alkali soluble cellulose derivative which can beshipped from one placeto another and stored until required. It avoidsthe necessity of providing a plane to make the xanthate at the pointwhere it is to be used. Accordingly, it makes the use of cellulosexanthate as flexible as nitrocellulose or cellulose acetate. The newproduct is utilizable, for example, in the preparation of threads,

bidium and caesium, and the halides include the filaments, transparentfilms, etc., and for the impregnation of materials such as paper, clothand wood and other porous substances.

Other derivatives of the cellulosic material may be prepared by reactingthe alkali metal cellulosate with a. substance capable of replacing thealkali metal in the cellulosate. For example, the alkali metalcellulosate'may be reacted with an etherifying agent such as an alkyl,aralkyl or an alkylene compound such as a halide, sulfate or sulfonatecontaining such a radical. For instance, alkyl halides, substitutedalkyl halides or aromatic halides in which the halogen group is readilyreactive may be used. Ethyl chloride and benzyl chloride are examples ofsuch compounds. Or .the alkali metal cellulosate may be reacted with anesterifyingagent such as an aromatic or aliphatic 'acyl halide such asacetyl halide, propionyl halide, butyryl halide or benzoyl halide or anacid anhydride such as acetic anhydride, etc. These reactions arepreferably carried out in the presence of liquid ammonia and undersubstantially anhydrous conditions.

An example of the foregoing, using benzyl chloride, is as follows:

Example 7.6 parts of weight of dried cotton linters were treated with5.9 parts of weight of potassium in 200 parts by weight of liquidammonia. The materials were allowed to stand in contact in the reactionvessel for 3% hours, after which the liquid was decanted and thecellulosic compound placed in a desiccator over sulphuric acid.Hydrolysis of the product showed that it contained 28.5 per centpotassium or approximately two atoms per Cs unit of cellulose.

Five parts by weight of the product obtained in Example 5 above wasplaced in a flask with 25.8 parts by weight of dry benzyl chloride, andprotected from moisture in the air by a drying tube containing calciumchloride. The flask was heated on a steam bath and was shakenoccasionally duringa period of 20 hours. The product was then washedseveral times with alcohol and water, and finally dried. The product wasonly slightlyv soluble in organic solvents but was completely insolublein cuprammonium solution, which indicates that it was no longercellulose. Presumably it was a benzyl cellulose of a low degree ofbenzylation.

Where it is desired to prepare ethyl cellulose the alkali metalcellulosate is treated with an excess of ethyl chloride and allowed tostand at room temperature or heated for several hours. The product isinsoluble in cuprammonium solution, and its solubility in organicsolvents, such as toluol or benzol, will depend on the degree ofethylation attained.

In carrying out the reactions indicated above, it is important, duringthe reaction and afterwards, to protect the contents of the reactionvessel from moisture and air since the alkali metal cellulosates arevery sensitive to hydrolysis and oxidation. The process may be carriedout with moisture present but with a sacrifice of alkali metal andalkali cellulosate.

The swelling agents referred to herein should be ones that aresufficiently soluble in liquid ammonia and that do not react with theammonia or with the other ingredients present or products formed. Alkalimetal and ammonium halides, thiccyanates or nitrates are examples ofsuitable swelling agents. The alkali metals referred to herein includesodium potassium, lithium, ru-

chlorides, iodides, bromides and fluorides.

This application is a continuation in part of my co-pending application670,040 and filed May 8, 1933. No claim is made herein to thepreparation of the sodium cellulosate itself since this is claimed in myapplications Serial Nos. 670,039 filed May 8, 1933 and 177,156 filedNovember 29, 1937.

In preparing the alkali metal cellulosate any of the well known types ofcellulose may be used, such as cotton, cotton linters, wood cellulose,regenerated cellulose, purified ramie, or partially substitutedderivatives of cellulose containing'at least one hydrogen atomreplaceable by'alkali metals. In using the term cellulosic materials inthe appended claims, it is intended to include such substances. v

- I claim: 1

1. A method of preparing stable cellulose derivatives which comprisesproviding an anhydrous alkali metal cellulosate and reacting the samewith a compound capable of replacing alkali metal in the saidcellulosate under substantially anhydrous conditions.

2. A method of preparing stable cellulose derivatives' which comprisesproviding an anhydrous alkali metal cellulosate and reacting'the same inthe presence of liquid ammonia with a compound capable of replacingalkali metal in the said cellulosate under substantially anhydrousconditions.

3. A method of preparing stable cellulose derivatives, which comprisestreating cellulosic material with alkali metal dissolved in liquidammonia and reacting the resulting product with a substance capable ofreplacing alkali metal in the said resulting product.

4. A method of preparing stable cellulose derivatives, which comprisestreating cellulosic material with alkali metal dissolved in liquidammonia and reacting the resulting product in the presence, of liquidammonia with a substance capable of replacing alkali metal in the saidresulting product.

5. A method of preparing stable cellulose derivatives, which comprisestreating cellulosic material with alkali metal dissolved in liquidammonia, said treatment being conducted in a substantially anhydrousatmosphere, and reacting the resulting product with a substance capableof replacing alkali metal in the said resulting product.

6. A method of preparing stable cellulose derivatives, which comprisestreating cellulosic material with alkali metal dissolved in liquid am-"monia, said treatment being conducted in a substantially anhydrousatmosphere and at about the temperature of the boiling point oi liquidammonia at atmospheric pressure, and reacting the resulting productwithan agent capable of replacing alkali metal in the said resultingproduct.

7. A method of preparing stable cellulose derivatives, which comprisestreating a cellulosic material with a solution of an alkali metal inliquid ammonia .in the presence of a compound tending to cause thecellulose to swell, and reacting the resultant product with a substancecapable of replacing an alkali metal in the said resulting product.

8. A method of preparing stable cellulose derivatives, which comprisestreating a cellulosic material with a solution of an alkali metal inliquid ammonia in the presence of one or more salts of the groupconsisting of alkali metal or ammoniumhalidw, thiocyanates and nitrates,and reacting the resultant product with a' substance capable ofreplacing an alkali metal in the said resulting product.

5. 9. A method oi'preparing stable cellulose xanthate which comprises,providing an anhydrous alkali metal cellulosate and reacting the samewith carbon bisulfide, under conditions where moisture is excluded.

10. A method of preparing stable cellulose xanthate which comprisestreating cellulosic material with metallic alkali metal dissolved inliquid ammonia and reacting the resulting product withcarbon bisulflde.1

11. A method of preparing stable cellulose xanthate which comprisestreating cellulosic material. with metallic alkali metal dissolved inliquid ammonia and under essentially anhydrous conditions, and reactingthe resulting product with carbon bisulflde.

12. A method of preparing stable cellulose xanthate, which comprisestreating cellulosic material with alkali metal dissolved in liquidammonia, such treatmentbeing conducted at about the temperature of theboiling point of-liquid amresulting product with carbon bisulphide.

.13. A method of preparing stable cellulose xanthate, which comprisestreating cellulose with alkali metal dissolved in liquid ammonia, suchtreatment being conducted in a substantially anhydrous atmosphere and atabout the temperature of the boiling point of liquid ammonia atatmospheric pressure, and reacting the resulting product with carbonbisulphide. v w t 14. A method of preparing cellulose xanthate,

which comprises treating a cellulosic materialfin the presence of acompound tending to cause the cellulosic material to swell, with alkalimetal dissulting productwith carbon bisulfide.

15. A method of preparing cellulose xanthate, which comprises treatingan alkali metal celluloifying agent.

sate with carbon bisulfide, in the presence of one or more salts of thegroup consisting of alkali metal or ammonium halides, thiocyanates andnitrates. f

' 16. A method of preparing stable cellulose xanthate, which, comprisessuspending cellulosic alkali metal and sodium iodide, permitting swell-.ing of the cellulose material, reacting the result- 7 ing product withcarbon bisulflde, and removing excess ammonia.

17. A methodof preparing stable cellulose xanthate, which comprisessuspending cellulosic material in liquid ammonia containing metallicalkali metal and sodium iodide, said alkali metal being present inquantity sufiicient to replace from about one to about three atoms ofhydrogen I per Co unit of cellulose, permitting swelling of thecellulose material, reactingthe resulting'product with carbon bisulflde,and removing excess am- 'monia. 7 j

18. A method of preparingstable cellulose xan= thate, which comprisessuspending cellulosic material inliquid ammonia containing metallicalmonia at atmospheric pressure, and reacting the solved in liquidammonia, and reacting the rematerial in liquid ammoniacontainingmetallic kali metal and sodium thiocyan'ate, permittingswelling of the cellulosic material, rejactingthe resulting product withcarbon bisulflde, and re- .moving excess ammonia. l 19. A method of;preparing stable cellulosede rivatives, which comprises providing ananhydrous alkali metal cellulosate, subjecting the alkali metalcellulosate to the action of aswelling agent of thegroup consistingofalkali metal or ammonium halides, thiocyan'ates and nitrates. andreacting the same fwith a compound capable of, replacing alkali metal inthe said cellulosate under substantially anhydrous conditions. I

20. "A method of preparing stable, cellulose xanthate, which comprisesproviding anhydrous alkali metal cellulos'ate, subjecting the 'alagentof the group consistingoi alkali metal or ammonium halides,thiocyanates, and nitrates,

, and reacting the samejwith carbon bisulfldaunder conditionswheremolstureis excluded. 7

t 21. A method of preparing stable cellulose derivatives,which'comprises treating cellulosic material with alkali metal dissolvedin liquid ammonia and reacting the resulting product with a substancecapableof replacing alkali metal in the said resulting product, saidreaction being under conditions where moisture is' excluded- 22. Amethod of preparing stablecellulose xanthate, which comprises treating'cellulosic'material with alkali metal dissolved in liquid ammonia andreacting the resulting product with carbon kali metal cellulosa'te tothe action of a swelling 1 bisulfide under conditions .wheremoisture isexcluded. I

23. A method of pre'paring a cellulose ether which comprises-providingan anhydrous alkali metal cellulosate and reacting the same with anetherifying agent under conditions where moisture is substantiallyexcluded.

24; A method of preparing cellulose ethers which comprises treating.cellulosic material with metallic alkali metal dissolved in liquidammonia and reacting the resulting product with an' ether- 25. A methodof preparing a cellulose ether which comprises providing an anhydrousalkali metal cellulosate'an'd reacting the samewith an alkyl halideunder conditions where moisture is substantially excluded. e v 1 26. Amethod of preparing a cellulose ether which comprises; providing ananhydrous alkali metal cellulos'ate and reacting the same with 'anaralkyl halide under conditions where moisture is substantiallyexcluded. p p

27, A method of preparing stablecellulose derivatives, which" comprisestreating cellulosic material with alkali metal in liquid ammonia, re-

moving the excess ammonia and reacting the resulting product with asubstance capable of re- 1 placing alkali metal in the said resultingproduct.

28'. A method of preparing cellulose'xanthate,

which comprises treating cellulosic material with metallicalkali metalin liquid ammonialre- "moving the excess ammonia and reacting'theresulting product with carbon bisuliide.

SCHERER, JR.

